Spatial distribution of inorganic nitrogen contents of marsh soils in a river floodplain with different flood frequencies from soil-defrozen period

Contents of inorganic nitrogen ([graphic removed] and [graphic removed]) in soil profiles were measured in five typical zones (including permanently flooded floodplain (B), 1-year floodplain (O), 5-year floodplain (F), 10-year floodplain (T), and 100-year floodplain (H)) from Huolin River floodplain in Erbaifangzi, Jilin Province of China, in the soil-defrozen period (May of 1999). Contour maps and profile maps were constructed to describe the spatial distributions of [graphic removed] and [graphic removed] in order to identify the influences of flood frequencies on them. Results showed that [graphic removed] generally increased with depth in soil profiles from the five areas, but [graphic removed] contents in T or H areas significantly differed from those in other areas. For [graphic removed] , with the exception that there was a significant cumulative peak (6.77 ± 0.08 mg kg⁻¹) at 15-cm depth (10-20 cm) in B area, no significant difference was observed between [graphic removed] contents in soil profiles from the other four areas. The horizontal distributions of [graphic removed] and [graphic removed] in top soils (0-10 cm) were different in the five areas, which were greatly influenced by flood frequencies. The highest content of [graphic removed] or [graphic removed] did not appear in B area but in the floodplain with certain flood frequency. For example, [graphic removed] content (16.81 mg kg-¹) in 5-year floodplain wetland was highest, and the highest content of [graphic removed] (1.69 mg kg-¹) appeared in 1-year floodplain wetland. In addition, [graphic removed] contents were significantly correlated with soil pH, and [graphic removed] contents had significant correlation with inorganic carbon, but there were no significant correlations between inorganic nitrogen and other selected soil properties.